All Big Six Timing and vacuum questions.

Relates to all big sixes

fox81

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Hey All,
Im trying to tune my new yfa carb i got from Mikes. Im new to this so i need some help.

I am trying to get a ported vacuum reading when giving it some throttle but my gauge isnt reading anything. I am tapping into the port at the bottom of the yfa. Is this the correct spot? This is where my vacuum advance has been plugged in. Now im thinking it wasn't working at all.

I don't see any other port to use. Maybe the hot air auto choke port? I had it plugged but took thw plug out to see if it would run better. I was thinking of getting a breather filter for it.

Any Help would be appreciated.20211023_122730.jpg20211023_122527.jpg20211023_122537.jpg
 

bubba22349

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Yes the lower vacuum tap at the carb base is the right one to use for ported distributor vacuum advance. I see you are not using a stock type air cleaner. The upper tap on the side of carb is supposed to hooked up to the base of the air cleaner so that it can drawn filtered air for the (this tap is a controlled vacuum leak to draw hot air from the exhaust manifold) through the chokes hot air stove pipe would looks like you don't have hooked up either. Good luck
 

fox81

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Thanks Bubba!

I have an electric choke so im not sure if i should just plug the hot air intake. I did have it plugged but i didnt seem to make a difference.

Im trying to figure out why i have no vacuum at the port for vac advance at the base of the carb while throttling. The truck seems to be running ok but im sure this is needed.
 

bubba22349

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Yes you have an electric choke these Ford systems were hooked up to the Stator on your Alternator for their power about 8 volts. But they also need to have a hot air tube going down to the exhaust system to work correctly (warm up the thermostatic Spring causing the choke blade to open up fully) do you see the threaded boss in the side of the choke housing? There should be a threaded fitting in that hole this is to hook up the hot air pipe from the exhaust manifold or in your case with heaters you can coil a brake line around one to the header tubes or they make a simple aftermarket repair kit in the "Help Section" of your local auto parts store. The upper hose nipple can't really be capped off it needs to draw air in from a clean source which then pulls the hot air in from the lower stove pipe.

You won't see any vacuum signal at the hose nipple at the base of the carb at Idle or low RPM's only when the engine is producing a higher vacuum signal, but it is possible to have used the wrong type carb base gasket that maybe doesn't have a clear vacuum path. Good luck Edited for some corrections and additional info. The Carter YFA Choke system and parts hook ups. https://www.carburetor-blog.com/knowledge-base/carter-yf-yfa-choke-system/
 

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fox81

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thanks.
i pulled the carb and compared it to my old yfa. i can blow air into the carb from that vac port on the old one, and could see and feel the holes the air was coming out from.

The new carb has no holes that i can find also i cant blow into it. tried some carb cleaner and it also goes nowhere. Wonder why they would put a port there with no path. Maybe im missing something..
 

THE FRENCHTOWN FLYER

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Maybe im missing something..
Yup
You're missing the hole. It was omitted - probably erroneously - at manufacture.
Measure the height of the hole on your old carb and try to match the new carb with a hole that has the same height entry point and diameter.
Your truck will run noticeably better.
 

bubba22349

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[Fox81 said] Maybe im missing something..

X2 yes sure sounds like it Can you take some pictures of both of the carb base's? I noticed in your above last picture a threaded opening in the carb adapter plate is that open into the intake manifold too? Also I edited my above post to correct some errors in my crappy spelling & sentence construction etc. and also add some more info.
 

fox81

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Yes Thank you!

That port was blocked off inside.
After some research i decided to go with full manifold vacuum for the advance. im just going to plug off the intended va port.
Now i just have to figure out the best way to time it using manifold vac.
 

bubba22349

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All you do is to plug off the vacuum line when your setting the base timing same as you would before. Like say to 10 degrees of base timing. Good luck
 

Frank

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Fox81. An incorrect carb body-to- base gasket can block the ported vacuum output. (ask me how I know!) Verify the hole in the throttle bore that connects to the ported vacuum: with the choke open and the throttle closed against the idle speed adjustment screw, look into the bottom of the carb. (it will have to be in your hand, you're looking from the engine side). Slowly open the throttle, and watch the part of the round blade that is opening away from you, toward the air filter side. As soon as you have opened it only a few degrees, a small hole should appear in the side the of the bore, approximately above the port where the vacuum line hooks up. That is the ported vacuum slot. If it is not there (I would be very mystified if it is not there), or if it is there, and does not connect to the external port- notify Mike. I have never had to do a return to Mike's carbs, but his stuff is spot on, he is a veteran carb mechanic. When you spray brake clean into the vacuum line port, it should be shooting out of this small hole in the throttle bore, and nowhere else. If it is not, the carburetor is faulty, probable cause, an incorrect gasket blocking the channel.
I do not think you will be happy with using manifold vacuum for the timing advance. Set the base timing-with the advance disconnected-, reconnect the line, and your idle will go up, significantly. Turn the idle speed down to where you want it, verify your mixture is set right, then go the the tailpipe and listen to the exhaust. It will be very quiet because of the early timing. that you can live with. But you may hear occasional misfires, randomly scattered. You will not be able to tune those misfires out with the timing that advanced at idle, the early timing is the cause.
 

fox81

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Thanks Frank!

Yes i took the carb off and blew into the port and there is no air passage that I can find with throttle open or closed. No holes like my older yfa. Im thinking its factory mess up. I verified the gasket and the holes line up. On my older carb the port goes right into the bore of the carb where i can pit finger over it to block air when i blow into it. The new yfa has no holes like this.

So i decided to shoot for manifold vacuum for the advance to see if i can make it work. Id rather not go through the hassle of shipping it back.

Ive read a few heating debates on manifold vs ported advance. It seems manifold advance might be ok. Just have to deal with the timing and the idle going up. Im still learning, but it seems there is a balance to be had. I have an inline advance restrictor that was factory. I wonder if i can use this to my advantage. Also I'm looking into recurving the dizzy?..
 

fox81

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Yup
You're missing the hole. It was omitted - probably erroneously - at manufacture.
Measure the height of the hole on your old carb and try to match the new carb with a hole that has the same height entry point and diameter.
Your truck will run noticeably better.
Sorry I missed your response.
Are you saying drill hole? I thought about it but id probably try get manifold vac to work first. Id even try getting an exchange from mike first.

Have you or any one you know of done something like this?

Thanks
 

fox81

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Is it possible to drill the hole into the bore like the original carburetor?
It doesnt seem like the ported hole is a direct shot into the carb. I tried sticking a small rod/wire into the hole of my old yfa and it wont go in. On my old yfa there are two holes going into the carb from this port. spaced out by about 1/2", very small too.
 

THE FRENCHTOWN FLYER

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Sorry I missed your response.
Are you saying drill hole? I thought about it but id probably try get manifold vac to work first. Id even try getting an exchange from mike first.
YES, DRILL A HOLE. IN SOME CASES IT IS NECESSARY TO DRILL A CROSS CHANNEL TO COMPLETE THE PASSAGE AND THEN BLOCK OFF THE CROSS CHANNEL. CARB TECHS OFTEN USE A PIECE OF LEAD SHOT FOR THIS.
Have you or any one you know of done something like this?
Yes, I have made many modifications to carb passageways.
Desperate people do desperate things.

RE: manifold signal to distributor. I avoid that because at idle you are seeing full vacuum advance. Then when you accelerate you open the throttle and the manifold vacuum drops precipitously, dumping all the vacuum advance, and the car stumbles, falls in a hole as it were.
To mitigate the effects of this you could install a spark delay valve (SDV) in the vacuum line so the vacuum bleeds off slowly, giving the vehicle time to get up to speed. Try a #1 or#2 valve - I think it is color coded brown or grey.
 
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fox81

Active member
YES, DRILL A HOLE. IN SOME CASES IT IS NECESSARY TO DRILL A CROSS CHANNEL TO COMPLETE THE PASSAGE AND THEN BLOCK OFF THE CROSS CHANNEL. CARB TECHS OFTEN USE A PIECE OF LEAD SHOT FOR THIS.

Yes, I have made many modifications to carb passageways.
Desperate people do desperate things.

RE: manifold signal to distributor. I avoid that because at idle you are seeing full vacuum advance. Then when you accelerate you open the throttle and the manifold vacuum drops precipitously, dumping all the vacuum advance, and the car stumbles, falls in a hole as it were.
To mitigate the effects of this you could install a spark delay valve (SDV) in the vacuum line so the vacuum bleeds off slowly, giving the vehicle time to get up to speed. Try a #1 or#2 valve - I think it is color coded brown or grey.
I will give this a go if all else fails.
I believe i have a sdv installed already. I thought it was a restrictor but im pretty sure its an sdv now. Its black and off white. I took her for a spin and its running great so far.

Im at 18 btdc initial using a vacuum gauge to set timing and it jumps up to 44 when manifold vac is hooked up. vacuum is steady at 17-18. Idle doesnt seem to jump up too much when i hook up the manifold vac. I dont have the tach wired up yet so im curious to see that next.

Does any of this seem like it could use adjustment?
 

THE FRENCHTOWN FLYER

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I would back off the initial timing to 12 degrees. It sounds like it may be over advanced. Remember as RPM increases additional centrifugal advance will be added to your initial and vacuum advance.
 
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